Self-selection in a population-based cohort study: impact on health service use and survival for bowel and lung cancer assessed using data linkage

Abstract

BackgroundIn contrast to aetiological associations, there is little empirical evidence for generalising health service use associations from cohort studies. We compared the health service use of cohort study participants diagnosed with bowel or lung cancer to the source population of people diagnosed with these cancers in New South Wales (NSW), Australia to assess the representativeness of health service use of the cohort study participants.MethodsPopulation-based cancer registry data for NSW residents aged ≥45 years at diagnosis of bowel or lung cancer were linked to the 45 and Up Study, a NSW population-based cohort study (N~ 267,000). We measured hospitalisation, emergency department (ED) attendance and all-cause survival, and risk factor associations with these outcomes using administrative data for cohort study participants and the source population. We assessed bias in prevalence and risk factor associations using ratios of relative frequency (RRF) and relative odds ratios (ROR), respectively.ResultsPeople from major cities, non-English speaking countries and with comorbidites were under-represented among cohort study participants diagnosed with bowel (n = 1837) or lung (n = 969) cancer by 20–50%. Cohort study participants had similar hospitalisation and ED attendance compared with the source population. One-year survival after major surgical resection was similar, but cohort study participants had up to 25% higher post-diagnosis survival (lung cancer 3-year survival: RRF = 1.24, 95% confidence interval 1.12,1.37). Except for area-based socioeconomic position, risk factors associations with health service use measures and survival appeared relatively unbiased.ConclusionsAbsolute measures of health service use and risk factor associations in a non-representative sample showed little evidence of bias. Non-comparability of risk factor measures of cohort study participants and non-participants, such as area-based socioeconomic position, may bias estimates of risk factor associations. Primary and outpatient care outcomes may be more vulnerable to bias.Electronic supplementary materialThe online version of this article (10.1186/s12874-018-0537-3) contains supplementary material, which is available to authorized users.

Pathways to diagnosis of non-small cell lung cancer: a descriptive cohort study

“…19,26 45 and Up Study participants diagnosed with lung cancer were less socio-economically disadvantaged, healthier and less likely to live in major cities than all NSW residents aged ≥45 years diagnosed with lung cancer. 27 Hospital and emergency department use in the year prior to lung cancer diagnosis were similar between 45 and Up Study participants and all NSW residents; however, primary and outpatient care use could not be assessed. 27 Participants of cohort studies may differ from non-responders in their health literacy and health-seeking behaviours.…”

“…27 Hospital and emergency department use in the year prior to lung cancer diagnosis were similar between 45 and Up Study participants and all NSW residents; however, primary and outpatient care use could not be assessed. 27 Participants of cohort studies may differ from non-responders in their health literacy and health-seeking behaviours. This may result in differences in diagnostic pathways compared with the general NSW population with lung cancer.…”

Health services costs for lung cancer care in Australia: Estimates from the 45 and Up Study

“…However, we derived excess cancer costs by comparing individuals within the cohort and adjusted for key factors in regression analyses. A recent paper from the 45 and Up Study reported that study participants diagnosed with lung cancer had longer post-diagnosis survival, but the cohort had similar levels of hospital and ED use as the NSW population [41]. Furthermore, our cohort was comparable to the total population of lung cancer cases on most key factors.…”

Diagnostic and health service pathways to diagnosis of cancer-registry notified cancer of unknown primary site (CUP)

“…While 45 and Up Study participants are healthier on average than the general population, relative estimates calculated from within-cohort comparisons are valid. [34,35] Two data issues are also unlikely to have affected our within-cohort comparisons; firstly, the ED data mainly captured visits to metropolitan and large regional public hospitals (72% and 88% of ED presentations in NSW, respectively). [36,37] Secondly, some pathology services will be under-ascertained as MBS claims data only capture the three most expensive pathology items in an episode of care performed by a GP.…”

“…MBS item numbers 2, 3,23,35,36, 44, 52, 53, 54, 57, 2501, 2504, 2517, 2521, 2525, 2546, 2552, 2721, 2725, 5000, 5020, 5040, 5060). We further distinguished GP consultations for the preparation, contribution or review of a GP management plan or multidisciplinary/team care plan (MBS item numbers 721,723, 729, 731, 732, 735, 739, 743, 747, 750, 758, 820, 822, 823, 825, 826, 828, 830, 832, 834, 835, 837, 838, 900)…”